Organic esters stabilized with an alkali metal and an organic phosphite



United States Patent 3,461,153 ORGANIC ESTERS STABILIZED WITH AN ALKALIMETAL AND AN ORGANIC PHOSPHITE Clarence E. Tholstrup and Sarah J. Rush,Kingsport,

Tenn., assignors to Eastman Kodak Company, Rochester, N.Y., acorporation of New Jersey No Drawing. Filed July 19, 1965, Ser. No.473,234 Int. Cl. C07c 66/82, 65/80 U.S. Cl. 260-475 3 Claims ABSTRACT OFTHE DISCLOSURE Organic esters free from acid hydrogen atoms which aresubject to discoloration at elevated temperatures containing from about0.25 p.p.m. to 1000 p.p.m. of alkali metal atoms and from about 0.1p.p.m. to 200 p.p.m. of phosphorus atoms.

This invention relates to organic esters free from acid hydrogen atomsand containing alkali metal atoms and phosphorus atoms, whereby theseesters have greatly enhanced color stability against the effects ofprolonged exposure at an elevated temperature.

The presence of alkali metal atoms along with such esters has beencontemplated by disclosures such as U.S. 2,825,737, issued Mar. 8, 1958,U.S. 2,867,594, issued Jan. 6, 1959, U.S. 2,938,015, issued May 24,1960, and other similar disclosures.

The presence of phosphorus atoms along with such esters has beencontemplated by disclosures such as U.S. 2,867,594 and U.S. 2,93 8,015which are mentioned above, as Well as U.S. 2,612,515 issued Sept. 30,1952, U.S. 2,961,454 issued Nov. 22, 1960, U.S. 3,047,608 issued July31, 1962, U.S. 3,053,878 issued Sept. 11, 1962, U.S. 3,076,018 issuedJan. 29, 1963 and other similar disclosures such as French Patent1,306,356 and British Patent 676,553; also see British Patent 978,304.

It is an object of this invention to provide organic esters which remainfree from adverse coloration after prolonged exposure at elevatedtemperatures.

It is a further object to provide such esters which remain substantiallyfree from color even after being held in a molten condition for anextended period of time.

It is another object to provide such esters which contain very smalltraces of additives whereby there is no significant affect upon thesubsequent utility of such esterfor essentially all expected purposes.

It is a more particular object to provide dialkyl isophthalates anddialkyl terephthalates having these advantages.

Further objects are also apparent from this specification, including theclaims.

According to one preferred embodiment of this invention there isprovided a composition of matter having enhanced color stability uponexposure to elevated temperatures consisting essentially of an organicester of a compound having a hydroxy radical and an organic carboxylicacid, said composition being essentially free of acid hydrogen atoms andcontaining from about 0.25 p.p.m. to about 1,000 p.p.m. by weight ofalkali metal atoms and from about 0.1 p.p.m. to about 200 p.p.m. byweight of phosphorus atoms, said ester being capable of maintaining anAPHA color value no greater than about 25 after being heated for 15hours at 210 C. when containing 20 p.p.m. of an alkali metal compoundand 10 p.p.m. a phosphorus compound.

Examples of such organic esters include aliphatic esters ice or aromaticcarboxylic acids such as dimethyl terephthalate, dioctyl phthalate,ethyl benzoate, etc., fatty glycerides such as stearates, palmitates,laurates, acetin, etc., aliphatic esters of aliphatic acids such asethyl acetate, ethylene diacetate, butyl propionate, dimethyl adipate,dibutyl sebacate, diisopropyl succinate, octyl stearate, etc. Suchesters generally have molecular weights well under 1,000 and are notpolymeric. An especially great improvement is obtained when the ester isa dialkyl (1 to 4 carbons) ester of isophthalic or terephthalic acid,particularly as regards stabilizing such esters in the molten form aswhen stored in tanks or transported in railroad tank cars.

Examples of compounds which can be used to provide alkali metal atomsinclude salts of potassium, sodium, lithium and cesium, especially thesalts of organic acids such as the aliphatic and aromatic acid salts.Other compounds include the alkali metal alkoxides (16 carbons). Thealiphatic or aromatic acids from which these salts can be obtainedinclude aromatic and/or aliphatic substituents. Particular examplesinclude potassium acetate, potassium stearate, cesium propionate,lithium benzoate, sodium oxalate, potassium adipate, lithium butoxide,cerium propoxide, sodium methoxide, potassium isopropoxide, etc. Thepotassium salts, especially of aliphatic dicarboxylic acids (2-10carbons) give unexpectedly good results, particularly potassium oxalate.

Examples of compounds which can be used to provide phosphorus atoms areillustrated in the literature and many patents such as those mentionedabove and U.S. 2,841,608 issued July 1, 1958, U.S. 2,847,443 issued Aug.12, 1958, U.S. 2,860,115 issued Nov. 11, 1958, U.S. 2,893,961 issuedJuly 7, 1959, U.S. 2,951,826 issued Sept. 6, 1960, U.S. 3,039,993 issuedJune 19, 1962, U.S. 3,047,- 608 issued July 31, 1962, U.S. 3,000,850issued Sept. 19, 1961, U.S. 3,056,824 issued Oct. 2, 1962, U.S.3,082,189 issued Mar. 19, 1963 and others. Although all organicphosphites, phosphates and derivatives thereof are considered useful,the degree of effectiveness is dependent upon the class of compoundsemployed.

Illustrative phosphorus compounds include tri(2,2,4-trimethylpentyl)phosphate, neopentyl phenyl phosphite, neopentyloctadecyl phosphite, polymeric phosphites such as derived frombis(p-hydroxyphenyl)-2,2-propane(Bisphenol A) and pentaerythritol whichis commercially available, distearyl pentaerythritol diphosphite whichis commercially available, tris(nonylated)diphenylphosphite which iscommercially available, triphenyl phosphite, etc. An unexpectedlysuperior phosphite is 1,4-cyclohexanedi methylene bis(neomntylphosphite)which is disclosed in copending application Ser. No. 308,369 filed Sept.12, 1963, now U.S. Patent 3,283,037 by Herman E. Davis, entitled,Bis(cyclic 2,2-dimethyltrimethylene)-1,4-cyclohexanedimethylenePhosphite. Other useful compounds are given elsewhere herein as well asin the reference patents listed hereinabove.

This invention can be further illustrated by the following examples ofpreferred embodiments although it will be understood that these examplesare included merely for purposes of illustration and are not intended tolimit the scope of the invention unless otherwise specificallyindicated.

The following data were obtained using the identified additive compoundsin the specified parts per million by weight in dimethyl terephthalate,the stabilized composition being heated at 210 C. and the time in hourswas ascertained to develop an APHA color of 25 and of 75. The initialcolor in each case had an APHA value of 10,

TABLE I.STABILIZED DIMEIHYL TEREPHTHALATE Stability in hours Aged Agedto to APHA, APHA, Additives, 20 p.p.m. of alkali metal salt and p.p.m.Color Color of organic phosphite of 25 of 75 Item Number:

1 None (control) 1 2 Potassium oxalate and items 2, 3 or 4 below:

2 Tris(nonylated)phenyl-phosphito 20 50 3 Neopentylphenylphosphite 23 504 1,4-cyelol1exanedimethanol bis(neopentylphosphite) 34 50 TABLEII.DIMETHYL TEREPHTHALATE The especially preferred organic phosphitesare those which have at least two atoms of phosphorus and at least onering, all of which rings contain carbon atoms and at least one ringcontains a hetero phosphorus atom attached to adjacent hetero oxygenatoms thereby forming a heterocyclic ring. The most particularlypreferred and especially advantageous phosphites have at least two suchheterocyclic rings.

The following formulas are typical of the especially preferred cyclicphosphite esters of polyhydroxy organic compounds:

Stability in hours Aged Age to to APHA APHA Item Additive, color colorNumber 20 ppm. employed of 25 of 75 None (control) 1 2 2 Potassiumoxalate. 1 2 3 Sodium stearate 1 3 4. Sodium benzoate 1 2 5. Potassiumethoxid 1 2 6... Sodium ethoxide 1.5 8 7 Tris(uonylated)phenylphosphite.3 8 8 Ncopentylphenylphosphite 3 8 9lA-cyclohexanedimethanolbis(neopentylphosphite) 6 10 This inventionpermits the especially advantageous (1) CHPO storage of dimethylterephthalate (DMT) in a molten R C P OR condition prior to its use as areactant in the manufacture of highly polymeric linear polyesters suchas poly- 2 ethylene terephthalate or poly (1,4-cyclohexanedimethyl- (2)CH2C 0-CH: ene terephthalate). Thus, molten DMT containing 10 .m. ofotassium oxalate and 10 .m. of 14-c clopp p p p y CHz-C 0-0 1hexanedimethanol bis(neopentylphosphite) can be stored at 165 C. for 521hours before an APHA color value of 15 is obtained. This is unexpectedlygOOd and represents excellent stability against discoloration since evenafter 521 hours the color rating is unity whereas, the

same conditions without any additives results in a poor color ratinggreater than 8. The presence of 10 p.p.m. of potassium oxalate aloneresults in a color rating of 2 and the presence of 10 p.p.m. of thephosphite alone results in a color rating of 6. The combination of bothadditives produces the extremely low color rating of 1 which isexcellent. v

In practicing this invention it is important to avoid introducingcompounds containing acid hydrogen, e.g. NaHSO or Na H PO or the like.It appeans that acid hydrogen counteracts the beneficial effects ofhaving an alkali metal present.

Although especially valuable results of particularly surprisingusefulness are obtained employing potassium oxalate in combination with1,4-cyclohexanedimethanol bis(neopentylphosphite), this invention alsoprovides good results not expected from a consideration of the prior artas regards the other related additive combinations described hereinabovewhen employed to stabilize any of the organic esters as defined herein,e.g. bis(2-hydroxyethyl) terephthalate, etc.

where R and R each represents a hydrogen atom or an alkyl radical having1 to 18 carbon atoms, R represents a hydrogen atom, an alkyl radicalhaving from 1 to 18 carbon atoms or an aryl radical of the benzeneseries having from 6 to 12 carbon atoms, X represents a divalent organicradical composed of hydrogen, carbon and oxygen atoms having aliphaticor alicyclic carbon atoms attached to the adjacent -O atoms shown in theabove formula. Preferably X contains from 2 to 20 carbon atoms when itis monomeric in form. It is also advantageous when X is a polyether ofethylene glycol, propylene glycol, tetramethylene glycol, or the like,having a molecular weight up to about 800, e.g., from about 200 to about600. When monomeric, HO-X-OI-I represents glycols illustrated by 1,4cyclohexane-dimethanol, 2,2,4,4 tetramethylcyclobutanediol, ethyleneglycol, diethylene glycol, neopentyl glycol, etc. In the above formulas,n is a small integer (usually less than 7) and m is an integer of from 1to a value such that the compound has a molecular weight no greater thanabout 4,000.

Although X represents a divalent radical, it can be more complex in thatit can be derived from a triol, tetrol, etc. For example, X canrepresent:

or it can be derived from a tetrol in an analogous manner. Moreover,many of these compounds include terminal constituents derived frommonohydroxy organic compounds, e.g., alcohols or phenols as covered bythe formula R"OH such as lauryl alcohol, stearyl alcohol, ethyl alcohol,phenol, cresol, etc.

Among the most advantageous phosphorus compounds are those cyclicphosphite esters having sterically hindered structures such as thosederived from neopentyl glycol, 1,4-cyclohexanedimethan01,2,2,4,4-tetramethylcyclobutanediol-1,3, etc. The most especiallyadvantageous compound is disclosed in the above-mentioned Davisapplication Serial No. 308,369 filed on September 12, 1963.

In the specification reference is made to an APHA color rating. The APHAcolor standard is described in the Standard Methods for the Examinationof Water by American Public Health Association, th edition, pages 87-89.The APHA value is based upon the p.p.m. platinum present in an aqueoussolution of platinum-cobalt chloride. The APHA color rating ranges frombelow 25 (essentially colorless) to 500, a dark yellow. APHA values of75 indicate that a slight yellowness is visibly present in the sample.

Although the invention has been described in considerable detail withreference to certain preferred embodiments thereof, it will beunderstood that variations and modifications can be effected withoutdeparting from the spirit and scope of the invention as describedhereina'bove and as defined in the appended claims.

We claim:

1. An organic ester selected from the group consisting of dialkyl (1 to4 carbon atoms) isophthalates and dialkyl (1 to 4 carbon atoms)terephthalates, said ester stabilized by (A) about 0.25 p.p.m. to about1000 p.p.m. by weight of alkali metal atoms selected from the groupconsisting of potassium, sodium, lithium and cerium, said alkali metalatoms being provided by at least one alkali metal carboxylate having 2to 18 carbon atoms or alkali metal alkoxide having 1 to 6 carbon atoms,and (B) about 0.1 p.p.m. to about 200 p.p.m. by weight of phosphorusatoms, said phosphorus atoms being provided by 1,4-cycl0-hexane-dimethylene-bis(neopentyl phosphite), tris(nonylated phenyl)phosphite, or neopentyl phenyl phosphite.

2. Dimethyl terephthalate stabilized by (A) about 0.25 p.p.m. to about1000 p.p.m. by weight of potassium atoms provided by potassium oxalate,and (B) about 0.1 p.p.m. to about 200 p.p.m. by weight of phosphorusatoms provided by 1,4-cyclohex-ane-dimethylene-bis(neopentyl phosphite).

3. The composition of claim 2 wherein said potassium atoms and saidphosphorus atoms are each present in amounts of about 10 p.p.m.

August 12, 1969 3: Dated Patent No.

lnvemods) Clarence E. Tholstrup; Sarah J. Rush I: is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 2, line 24, "ceriunfl should read cesium Column 6, Claim 1, line13, cerium" should read cesium SIGNED AND SEALED JUL? I910 (SEAL)Attest:

Edward M. Fletcher, Jr.

A WILLIAM E. SOHUYLER, J'R. uestmg 1cm Commissioner of Patents

